-- Flight Is the Seventh Consecutive Successful Minotaur I Space
                               Launch --

    -- Mission Completes Third Minotaur-Family Launch In Last Four
                               Months --

DULLES, Va.April 24, 2007--Orbital Sciences Corporation (NYSE:ORB) announced today that its Minotaur I rocket successfully launched the Near Field InfraRed Experiment (NFIRE) spacecraft for the Missile Defense Agency (MDA) and U.S. Air Force. The mission originated earlier today from the Mid-Atlantic Regional Spaceport (MARS) launch facility on Wallops Island, Virginia. At approximately 2:47 a.m. (EDT), the rocket's first stage ignited, beginning the mission into low-Earth orbit. Approximately 9 minutes later, the Minotaur I deployed the NFIRE spacecraft in its targeted orbit of approximately 250 km (135 nautical miles) by 450 km (245 nautical miles) above the Earth's surface at an inclination of 48.2 degrees to the equator.

Today's mission was the second Minotaur I launch from the MARS facility, following the initial mission conducted just over four months ago on December 16, 2006. The mission was the seventh flight of the Minotaur I space launch vehicle (SLV), and the 13th overall launch of the Minotaur program since 2000, all of which have been successful.

"We are very pleased to once again provide reliable, on-schedule launch services for the U.S. Air Force's Space and Missile Systems Center (SMC)," said Mr. Ron Grabe, Orbital's Executive Vice President and General Manager of its Launch Systems Group. "We are now focused on the three upcoming Minotaur launches in the second half of this year, including two Minotaur II long-range target vehicles scheduled for MDA flights this summer from Vandenberg Air Force Base, California, and another Minotaur I mission scheduled to be launched from Wallops late in the year carrying the Air Force's TacSat-3 spacecraft."

The overall launch service and management for the Minotaur I vehicle was provided by the U.S. Air Force Space and Missile Systems Center's, Space Development and Test Wing (SDTW) at Kirtland Air Force Base, New Mexico.

Most of the Minotaur launch vehicle hardware originally intended for the NFIRE launch vehicle was used to integrate and launch the TacSat-2 spacecraft in December 2006. Therefore, Orbital built and integrated a new launch vehicle to support NFIRE in less than 11 months from contract initiation until launch.

NFIRE is a low-Earth orbiting, 494 kg (1,089 lbs) satellite with an onboard Track Sensor Payload (TSP) and TESAT Laser Communications Terminal (LCT) as the primary payloads. The spacecraft is part of MDA's Kinetic Energy Boost-Phase research program. NFIRE will gather near-field, high-resolution phenomenology data that will assist in the development of boost-phase intercept systems. The spacecraft has a two-year design life, during which various data collection missions will be conducted, including gathering data during the flight of launch vehicles during their boost phase. As part of this testing, the next two Minotaur II target vehicles will be launched from Vandenberg later this year.

The launch of the Minotaur II NFIRE target vehicles will demonstrate new technologies for the Minotaur family of launch vehicles that are applicable to responsive launch capabilities, such as will be needed to support Operationally Responsive Space (ORS) and other rapid-response launch requirements. Because of the complexities of the upcoming missions, the Minotaur II vehicles will have specific trajectory information uploaded only 90 minutes prior to launch, as may also be necessary for some ORS space launch missions.

Minotaur I launches have put a total of 25 satellites into orbit. This is the seventh consecutive successful launch of the Minotaur I vehicle since January 2000, and there have been six successful Minotaur II launches during that same period as well. Over the next three years, Minotaur rockets are currently manifested to conduct another six launches.

About Orbital's Minotaur Product Line

Orbital's Minotaur product line was developed under the U.S. Air Force's Orbital/Suborbital Program (OSP). The initial five-year OSP contract was competitively awarded to Orbital in 1997 and the company also won the follow-on 10-year OSP-2 contract in 2003. The Minotaur I space launch vehicle design used in today's NFIRE launch is the original member of Orbital's Minotaur family of launch vehicles, which includes both space launch vehicle designs and long-range suborbital vehicles for missile defense and other specialized launch missions.

The Minotaur vehicles are the only proven launch vehicles currently capable of supporting the Department of Defense's evolving ORS launch requirements. This capability was demonstrated during the TacSat-2 launch in December 2006. Even though it was the first launch from Wallops' MARS facility and the first flight of a new fairing configuration, the mission was performed in less than seven months from contract initiation to launch.

The TacSat-2 mission also demonstrated the ability of Minotaur vehicles to stand on alert awaiting orders to launch when the original launch date was slipped five days after the vehicle was in a launch-ready posture. The Minotaur vehicles are also specifically designed to be capable of launching from all U.S. spaceports, including government and commercial launch sites in Alaska, California, Florida and Virginia. Due to the minimal amount of specialized infrastructure that is required to support Minotaur launches, they can also be employed at other U.S. launch sites.

The Minotaur I space launch configuration combines Orbital's commercial launch vehicle technologies, including upper stage rocket motors, structures, avionics and other elements, with government-supplied lower-stage rocket motor stages to create responsive, reliable and low-cost launch systems for U.S. Government-sponsored spacecraft. It can place up to 1,300 lbs into low- Earth orbit.

The Minotaur family of launch vehicles utilizes standardized avionics and subsystems, mature processes and experienced personnel to make them reliable and cost effective. In addition to the Minotaur I space booster, Orbital's Minotaur product line also includes:

    --  Minotaur II TLV - A three-stage suborbital rocket used as a
        target vehicle for testing U.S. missile defense systems and
        related missions. There have been six successful Minotaur II
        missions, the most recent being a target launch for MDA on
        March 20, 2007. Two additional launches are scheduled this
        year, both of which are intended to be observed by the NFIRE
        spacecraft as it passes overhead in orbit;

    --  Minotaur III TLV - A three-stage suborbital rocket, Minotaur
        III can deliver suborbital technology demonstration payloads
        of up to 6,500 lbs. or serve as a target vehicle for testing
        U.S. missile defense systems and similar missions;

    --  Minotaur IV SLV - A heavier-lift four-stage space launch
        vehicle using retired Peacekeeper rocket motors, capable of
        launching U.S. Government-sponsored satellites weighing up to
        3,800 lbs. into low-altitude orbit. The first Minotaur IV
        mission is currently under contract to launch the Space-Based
        Surveillance System (SBSS) satellite for the U.S. Air Force.
        Two Minotaur IV vehicles are also manifested in a suborbital
        configuration to launch Hypersonic Test Vehicles for DARPA;
        and

    --  Minotaur V SLV - An enhanced-performance version of the
        Minotaur IV space launch vehicle that may be used to launch
        government satellites into higher-energy orbits for missions
        related to space exploration and other activities beyond
        low-Earth orbit.

    About Orbital

Orbital develops and manufactures small space systems for commercial, civil government and military customers. The company's primary products are satellites and launch vehicles, including low-orbit, geosynchronous-orbit and planetary spacecraft for communications, remote sensing and scientific missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense boosters that are used as interceptor and target vehicles. Orbital also offers space-related technical services to government agencies and develops and builds satellite-based transportation management systems for public transit agencies and private vehicle fleet operators. More information about Orbital can be found at http://www.orbital.com.

Notes to Editors:

High-resolution photos of the Minotaur rocket are available on
 Orbital's website at:
 http://www.orbital.com/NewsInfo/Images/SpaceLaunch

More information about the Minotaur/NFIRE mission is available at the
 following sites:
 http://www.orbital.com/SpaceLaunch/Minotaur
 http://www.gd-ais.com

    CONTACT: Orbital Sciences Corporation
             Barron Beneski, 703-406-5528
             Public and Investor Relations
             Beneski.barron@orbital.com

    SOURCE: Orbital Sciences Corporation